1. Field of the Invention
The invention relates to a bicycle chain ring assembly, more particularly to a variable speed-type bicycle chain ring assembly which has a lower manufacturing cost than the prior art.
2. Description of the Related Art
FIG. 1 is an illustration of a conventional single speed-type bicycle chain ring. The bicycle chain ring comprises a sprocket (10) to be provided on a crank pin (A) of a crank (12). The sprocket (10) is usually stamped from a metal plate (not shown). A high scrap rate is usually obtained when fabricating the sprocket (10), thereby increasing its manufacturing cost.
Referring to FIG. 2, a conventional variable speed-type bicycle chain ring assembly is shown to comprise a hub member (13) and a pair of sprocket ring members (14, 15). The hub member (13) is to be secured to a crank (not shown). The sprocket ring members (14, 15) have different diameters and are provided with a plurality of angularly spaced inward projections (141, 151). The inward projections (141, 151) of the sprocket ring members (14, 15) are secured on two sides of the hub member (13) adjacent to the distal ends of the radial arms (131). As with the sprocket (10) shown in FIG. 1, the sprocket ring members (14, 15) are also stamped from a metal plate. Fabrication of the sprocket ring members (14, 15) yields high scrap metal rates (i.e, the material efficiency is very low), thereby increasing the manufacturing cost of the bicycle chain ring assembly.